With any historical figure who has been studied as much as Robert E. Lee, there will be many points of view. Although various people take somewhat different views, we can say that a majority of scholarly opinion sees Lee as a great tactician but argues that he may have been somewhat less able as a strategist.
Lee is known for being able to win battles against larger Union forces. He is known for being bold in maneuver and willing to do unorthodox things to win battles. Both of these attributes can be seen in the Battle of Chancellorsville. There, Lee faced a superior Union force and, even so, split his command twice, allowing him greater flexibility and winning a great victory.
Of course, there are those who say that he could take this tendency to be aggressive too far. These critics look in particular to Gettysburg. They argue, for example, that he should never have ordered Pickett's Charge. However, the majority still sees Lee as a great tactician.
Lee's strategic vision is less praised. It is commonly pointed out that he invaded the North twice, with both invasions being repulsed. It is argued that he would have been better off if he had not mounted these invasions.
Whatever his faults, Lee was clearly one of the greatest generals of the Civil War.